The use of styrene-butadiene copolymer latex in portland cement compositions is known to improve the properties of such compositions. For example, U.S. Pat. No. 3,043,790 discloses that the addition to portland cement compositions of styrene-butadiene copolymer latexes of the type contemplated by the present invention, results in improved strength, especially when cured under adverse curing conditions, as well as enhanced flexibility, adhesion, and elongation at break. These latex modified portland cement compositions have found wide acceptance in the preparation and repair of highway and bridge deck construction.
Further, U.S. Pat. No. 3,895,953 discloses mixtures of hydraulic cement, sand, gravel, water and small amounts of a styrene-butadiene copolymer latex wherein such latex is utilized to reduce early slump loss of the mixtures, e.g. during transportation and handling of such mixtures.
The placing of concrete on vertical and/or overhead surfaces, e.g. concrete columns, piers, beams, soffits and bridge deck undersides, is also known in the art. Such applications require cement compositions which can be efficiently sprayed, e.g. by pneumatic means, onto the surfaces to be repaired or constructed. This process is known in the industry as "shotcreting" and "guniting". Special problems are encountered in utilization of cement compositions in such applications. More specifically, the use of prior known polymer latex modified cement compositions fail to provide a combination of adequate sprayablilty and required adhesion to the surface being coated while providing sufficient resistance to volume change.
It is the primary object of the present invention to provide cement compositions which can be effectively pneumatically sprayed onto surfaces to be repaired or constructed and which provide excellent bonding and resistance to volume change.